Sustainable Ecosystems
Ecology is the scientific study of the
abundance and distribution of organisms,
and of their interactions with their
Oikos = house
 Logos = to study
Ecology uses the scientific method of
hypotheses and deductions.
Good hypotheses generate predictions that
can be tested.
Experiments are designed to test the
If the data gathered does not support the
hypothesis, it is refuted or falsified.
An experiment cannot prove a hypothesis to
be true – rather they become strong
hypotheses if multiple experiments fail to
refute them.
Robert T. Paine
Zoologist Robert T. Paine, who coined the
term "keystone species," had an
unorthodox way of doing his work.
 It was unorthodox at the time because
most ecologists simply observed and
measured factors in nature and tried to
make conclusions from these.
Paine’s experiment
Instead of just observing the habitat of
the Pisaster ochraceus sea star, Paine
experimented by changing the habitat.
 Paine and his students from the
University of Washington spent 25 years
removing the starfish from a tidal area on
the coast of Tatoosh Island, Washington, in
order to see what happened to other
species when they were gone.
The sea stars are a major predator for
mussels on Tatoosh Island.
 With the sea stars gone, mussels took over
the area and crowded out other species.
 In this ecosystem, the sea star was the
keystone species.
Ecology is exciting!
Ecology has a long history of being a
historical science, and has only started to
become an experimental science in the
last 50 - 60 years.
 Many old ideas have not had a chance to
be tested thoroughly
 This makes ecology an exciting field of
study, because new discoveries can have
an enormous impact
Experimental Lakes Area
World renowned Canadian institution
 Only place in the world capable of doing
long-term, whole-ecosystem experiments
 Have studied such topics as:
◦ Effects of synthetic hormones on fish
◦ Impacts of flooding soils on mercury
contamination of fish
◦ How changing nutrient balance in freshwater
lakes affect blooms of toxic algae
◦ How acid rain affects lake ecosystems
What is meant when we say that
organisms interact with their
 The environment includes both biotic and
abiotic components.
 Biotic components are the living aspects
of the environment – other members of
the same species and members of other
Examples of biotic factors
Mice must be constantly vigilant to avoid
predation by owls and snakes
 Mice must also compete with other mice
for resources such as habitat space, food
and water, and access to potential mates
Abiotic factors
Abiotic components are the non-living
factors or conditions which are unique to
the ecosystem.
 These are usually conditions such as the
amount of rainfall, sunlight levels, wind
speed, soil temperature, nutrient levels,
oxygen concentration, type of substrate
Biotic and abiotic factors
Ecosystem Abiotic factors
Biotic factors
•Long cold winter season
•Warm summers
•Moderate rainfall
•Much precipitation falls as snow
•Snow insulates and protects
ground species
•Short growing season
•Few species
•Dominated by black spruice forests
and bogs
•Black bear, red squirrels, moose
•Many biting flies - blackflies,
mosquitoes, horseflies, deerflies
Coral reef
•Water temperature from 25–
•Water depth from 0 – 30 m
•Usually occur in tropical
•Substrate high in limestone
from bodies of coral
•High variety of marine life – corals,
sponges, fish, crabs, urchins
•Organisms sensitive to changes in
temperature and acidity
Rotting log
•Moist environment
•Low light levels
•Temporary ecosystem – lasting
less than a decade
•Bacteria, fungi, lichens, moss, some
•Beetles, insect larvae
•Provides cover for small vertebrates
like salamanders and skinks
Levels of organization
Depending on the question asked, an
ecologist might investigate at one or
more of the following levels:
A single member of a species
Sometimes this is difficult to define
◦ Eg: a colony of quaking Aspen (Populus tremuloides) in Utah has
been determined to be part of a single living organism, with an
interconnected root system. This makes it the heaviest organism
on the planet, estimated at 6000 tonnes. It is also likely the
oldest organism on the planet, approximately 80,000 years old.
◦ Eg: similarly, the honey mushroom colony is known to cover 8.9
km2 of forest in Oregon, making it the largest organism on the
earth by area
Q: How does a cave cricket find its way in and out of
it’s dark cave when it comes out to forage for food?
Groups of the same species living in one
a herd of caribou
a flock of Canada geese
the E. coli bacteria living in a person’s gut
all of the smallmouth bass living in a lake
They may compete for resources, and are
also more likely to combine their genes
during reproduction than with members
of other populations
Population ecologists ask questions at this
 Often the questions are about abundance,
density, population growth and limits on
Q: How does deforestation in Costa Rica
affect the maximum number and the
nesting success of migrating songbirds?
Groups of different species living in the
same area.
 Different species have different roles or
‘functions’ in a community
 Eg: some act as producers, others are
consumers and still others are
Imagine a herd of caribou
Now include the two species of grass that it feeds on in the
Now picture the many other species of sedges and grasses
that they trample in the process of grazing
Now imagine the species of beetles that feed on the same
species of grasses, the soil microorganisms, the ticks that live
on the hide of the caribou, and the birds that feed on those
ticks, and the beetles that feed on the dung of the caribou
This is a very simplified picture of a tundra community
Q: How does the presence of (or absence) of a tick
fungus affect the survival of a population of caribou?
Ecosystems are assemblages of interacting
communitites in the same general area, as
well as the abiotic factors that are
important for sustaining life.
 Ecosystems can be nested within other
 The size of an ecosystem can be as large
as a national park, or as small as a rotting
An Ecosytem ecologist might ask:
What role do insect populations play in
the health of salmon, bear and coniferous
trees in coastal ecosystems.
 What role do the nutrients in bat guano
(feces) play in the support of
nonphotosynthetic ecosystems in caves?
Most natural ecosystems are sustainable
 This means they have the ability to
maintain natural ecological conditions or
processes without interruption,
weakening, or loss of value indefinitely
 Artificial ecosystems are usually not
 They require input of energy to maintain
the biotic and abiotic factors
Energy in Ecosytems
All organisms need energy to survive and to
function – energy is ability to do work, such as
grow, repair, search for mates, search for food
 Ultimately, all of the energy on earth came from
the sun!
 But only a small part of the sun’s energy is
actually used directly by organisms.
◦ 30% is reflected by clouds back into space
◦ The other 70% is absorbed by the lithosphere,
atmosphere and hydropshere
◦ This is important because it warms the earth, and
produces weather and climate patterns
Energy in Ecosystems
Only a very small percentage of that 70% is
used for photosynthesis: ~0.023%
 Producers convert the sun’s energy into
chemical potential energy - into molecules of
sugar in a process called photosynthesis
 Both producers and consumers break these
sugars down using their mitochondria in a
process called cellular respiration
 This allows them to use the energy stored in
the sugars to grow and reproduce
Photosynthesis and Cell Respiration
carbon dioxide + water
sugar + oxygen
Cell respiration:
sugar + oxygen
carbon dioxide + water
Energy flow in a food chain
Consider the following food chain:
Pine cone (seeds)
red squirrel
In this food chain, some of the chemical energy stored
in the pine cone is passed through the red squirrel on
into the weasel and finally to the goshawk.
 In a food chain, only about 10% of the energy gained
and used by one level is passed on to the next
 Of all of the energy the pine tree has absorbed over its
lifetime, only some of it is now stored in the tissues of
the tree – most of it has been converted into heat and
can never be used by other organisms
Food Webs
Food chains do not exist in nature – instead they are
part of a much larger food web – even this example is
greatly simplified
Trophic Levels
Food Webs
Trophic Levels
Secondary consumers
Primary consumers
Primary producers
~90% energy lost as heat
~90% energy lost as heat
~90% energy lost as heat
~90% energy lost as heat
~90% energy lost as heat
Energy is lost at each level
This bull has eaten 100 kJ of stored
energy in the form of grass, and
excreted 63 kJ in the form of feces,
urine and gas. The energy stored in its
body tissues is 4 kJ. So how much has
been used up in respiration?
The energy released by respiration =
100 - 63 - 4 = 33 kJ
Only 4 kJ of the original energy
available to the bullock is available to
the next stage, which might be humans.
The efficiency of this energy transfer
efficiency = 4⁄100 × 100 = 4%
What should we be eating?
Pyramid of energy
Pyramid of numbers
Cycling of Matter
Carbon Cycle
Nitrogen Cycle
Phosphorus Cycle
Biotic and Abiotic Factors
Abiotic factors will determine which
species can live in an ecosystem
e.g.: cactus will thrive in desert, but maple trees will not
All species have a range of tolerance
 Outside this range of an abiotic factor
such as temperature, there is a zone of
 Outside this range, there is a zone of
Range of Tolerance
Distribution of a species
Each ecosystem has a set of abiotic
factors that allow certain species to live
Biotic Factors
The species that live or colonize an area
can determine the characteristics of that
area as well
◦ Grass plants produce no shade, but oak trees
◦ Lichen can gradually erode rock to form soil,
changing the types of plants that can live in an
Carrying Capacity
The upper limit of organisms that an
ecosystem can support for an unlimited
amount of time
 As population size increases, competition
for resources increases
 Individuals become more susceptible to
predation and disease
 Carrying capacity can change because
environmental conditions can change
Carrying Capacity
Biotic Interactions
Competition: between species, or within
 Predation: lynx-hare, owl-vole
 Symbiosis:
◦ Parasitism: brown cowbird
◦ Mutualism: lichen – algae and fungus
◦ Commensalism: caribou and mice
Terrestrial Ecosystems
A biome is a large geographic area that
has a characteristic climate (temperature
and precipitation) and set of biotic and
abiotic features
 In Canada, there are four major biomes
Temperate deciduous forest
Boreal forest
Mountain forest
Aquatic Ecosystems
Water covers more than
two-thirds of our planet
 97% of the water is salt
 Freshwater is available in
rivers, streams, lakes, and
 Some is stored as snow or
ice – these often act as the
source of freshwater rivers
Aquatic Communities
◦ Pelagic – light penetrates top few meters
◦ Abyssal – light is absent
Continental Shelf
◦ Inter-tidal – hear shore – many specially adapted
◦ Coral reefs – distinctive communities dominated by
coral, algae and plankton
◦ Lakes
◦ Rivers
◦ Wetlands – swamps, marshes, bogs and fens
Plants and animals in aquatic ecosystems have
adapted to abiotic conditions such as:
◦ Less oxygen available, which limits
◦ Water is 800 times denser than air,
making it difficult to move through
◦ Dramatic pressure changes , making it
difficult for species to travel to
different depths
Abiotic Factors in Lakes
 Amount
of light available
 Water temperature
 Oxygen levels
◦ Lakes are divided into zones which
are characterized by these abiotic
◦ Abiotic factors dictate the organisms
that will reside in each zone.
Types of Lakes
Oligotrophic – deep and cold, low
nutrient levels, producer populations are
limited, water very clear. (Lake Superior
is 200 m deep)
Eutrophic – shallow and warm, high
nutrient content, many photosynthetic
organisms, water is murky.
Oligotrophic lakes gradually become eutrophic.
Eutrophic lakes become shallow over time and
result in dry land.
The evolution from a oligotrophic lake to dry
land is called eutrophication.
This evolutionary change may take hundreds to
thousands of years.
Human waste can speed up eutrophication.
This fact was discovered by the ELA in the
1970s with some controlled experiments
The two basins of this lake
were separated by a plastic
curtain. The lower basin
received additions of carbon,
nitrogen and phosphorus; the
upper basin received carbon
and nitrogen only. The bright
green colour is from a surface
scum of algae resulting from
phosphorus additions.
The entire interconnected set of rivers, lakes
and groundwater in a large area
 The watershed that serves the area where you
live is called the Etobicoke Creek Watershed
 Formed by the Brampton Esker - a long, winding
ridge of sand and gravel deposited by glacial
meltwaters as glaciers retreated
 The esker rises north of Mayfield Road and runs
between Hurontario Street and Kennedy Road
south to Queen Street.
Ecosystem Services
Ecosystem services are the benefits
experienced by species (including
humans) that are provided by sustainable
ecosystems. Examples of services include:
atmospheric gas supply
climate regulation
water supply
food production
raw materials
waste treatment
soil erosion control
nutrient recycling
Gradual and predictable changes in the
composition of biotic and abiotic factors
following a disturbance
 Primary succession – occurs on bare soil
or rock – such as after a volcanic
 Secondary succession – following a
disturbance that does not necessarily
destroy the community – such as a road
cut or forest fire
The variety of life in an ecosystem
 Not only variety of different species, but
also genetic variation within a species
 Compare: a naturally-occurring forest
with a tree farm
 Threats to biodiversity include: habitat
destruction, climate change, air and water
pollution, overhunting and overfishing,
introduction of exotic species
Keystone species
One species in an ecosystem that links
together many different food chains
 Can be useful in determining the health of
an ecosystem
 E.g.: the black fly in Ontario
Species at Risk
When population levels fall below a
certain level, there are ecological
Special concern
Habitat Loss
Not only does the area of a habitat loss matter,
sometimes the fragmentation of a large area can
reduce sustainability
 Habitat loss and fragmentation is second only
to climate change as the most serious threat to
sustainability of ecosystems
 Songbirds native to Ontario migrate to south
and central America in the winter – as these
areas are deforested more each year, the birds
have less and less suitable nesting grounds when
they finish their migration
Habitat Fragmentation
Factors that improve the sustainability of habitat fragments
Poorer Option
Better Option
Large blocks support large
more stable populations and
One large area is better
because there is less outside
The closer fragments are, the
greater chance organisms will
be able to use the entire area
Wildlife corridors permit
migration between blocks
Access by road and trails can
increase pollution, hunting
and fishing
Introduction of Exotic Species
A species that is introduced (purposefully
or accidentally) which negatively impacts
the natural ecosystem
 Ontario examples:
Asian Carp
Zebra mussel
Asian Long-horned Beetle
Purple loosestrife
Controlling Exotic Species
Chemical control
◦ larvicides and pesticides
◦ may kill non-target species
◦ add harmful chemicals to the environment that may last for many
Mechanical Control
◦ physical barriers
◦ removal by hand
Biological control
◦ intentional introduction of a predator species which will target
only the invasive species
◦ not likely to eradicate introduced species, only reduce their
Release of any toxic material into the
environment – air, water, or ground
 Acid precipitation – sulfur dioxide,
nitrogen oxides released combines with
water vapour to form acid – this falls as
rain or snow
 Affects soil and water, productivity of
forests and lakes and ocean ecosystems,
buildings and bridges that are made of
Water Pollution
Oil spills and leaks occur hundreds of
times each year in Canada
 Many are considered small (measured in
hundreds of barrels of oil)
 Large oil spills like the Exxon Valdez or
the British Petroleum’s Deep Water
Horizon are more dramatic
 Both large and small spills have longlasting effects on the environment
Forestry Practices
Natural forests can maintain themselves
without human intervention
 If we use them as a resource, we must do
it in a sustainable way – so that the trees
do not limit habitat and allow for
regeneration of cut areas
 Three common types of forestry methods:
◦ Clear-cutting
◦ Shelterwood cutting
◦ Selective cutting
Soil Characteristics
Besides a mixture of minerals, nutrients,
and decomposing organic matter, soil is
also composed of many living things
including billions of microscopic
◦ Bacteria – both harmful (like tetanus) and
helpful (nitrogen-fixing bacteria)
◦ Fungi – mycorrhizal fungi surrond root hairs
of plants and help deliver water and nutrients
to the plant root
Soil Characteristics
Nutrient content
 Compaction and air spaces
 Water-holding capacity
 Acidity (pH level)
Soil differs in these factors depending on
how much humus, silt, sand, and clay it
Managing Soil Nutrients
When a food crop grows, the nutrients in
the soild are taken up by the plants and
locked in their cells and tissues
 When the crop is harvested, the nutrients
it contains (carbon, nitrogen, phosphorus)
are removed from that field and so need
to be replaced or the soil will not be
fertile enough to grow more crops
Natural - plant and animal waste
 Synthetic – usually contains some mixture
of nitrogen, phosphorus and potassium –
increased crop yields dramatically in the
1960s when they were first introduced
 Problems with concentrated fertilizers:
Leaching into groundwater
Stress out soil organisms
Soil becomes dependent on fertilizer
Soil becomes susceptible to erosion
Irrigation and drainage
Diverting water from an aquatic
ecosystem to a farmland is necessary if
precipitation is not reliable
 This can have negative consequences
 Wetlands and rivers can be harmed by
too much water being diverted for
Alternative Farming Practices
To reduce the impact of farming
No-tillage – ground is left undisturbed after harvest
– stumps of plants are decomposed to add nutrients
to soil, reduces compaction and water loss
Crop rotation – plots are not farmed with the same
crop every year – alternating between corn soybean
and wheat – reduces need for fertilizers
Crop selection – choosing crops best suited to the
growing location – for example drought resistant or
heat-tolerant plants would do better in hot dry areas
Pests and Poisons
A farm is a monoculture – only one
species is supported
 This maximizes food production, but is
 A lot of effort is made to reduce loss
from pests such as fungus, insects, and
competition from other weeds
 Pesticides are commonly used, which
work by causing physical or biological
harm to a pest
Problems with Pesticides
They are sometimes not specific and can
affect non-target species
 Pests often become resistant to pesticides
and so new ones constantly need to be
 Bioamplification – when toxins are
absorbed by organisms at greater levels
than they are excreted
Pollutants (especially ones that are fat-soluble)
increase in concentration in each trophic level –
DDT, methyl mercury, persistent organic
pollutants (POPs)
 Even when released in very low concentrations
into the environment, with each step up the
food chain pollutants are not excreted because
they are locked in the fat tissues
 Therefore these get passed on to the next
trophic level in ever greater quantities
Robert T. Paine
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